Over the last few years, a number of companies have developed raw materials and components for vacuum cleaner bags to replace the older single layer paper bag and the well-known two-ply bag, having a downstream filter paper and an upstream tissue paper, with bags having upstream layers of either wet-laid tissues or fibrous fleeces such as meltblown (MB) ultra-fine webs occasionally referred to herein as "filtration grade MB fleece." With the advent of electrostatically charged MB fleeces, it has been possible to produce bag laminates with filtration efficiencies on the order of 99.8-99.9% to fine dust at a moderate airflow. However, conventional MB webs are essentially flat filters. Additionally, the fine dust filtering layer either is exposed directly to incoming dust particles or is positioned immediately downstream of a very open, abrasion protective tissue which only filters the largest of dust particles. Consequently, filter structures that utilize MB webs quickly load up with dust, reduce the air suction, and lose further dust pick up ability by the vacuum cleaner. Conventional dust bags generally have an air permeability of 200 to 400 L/(m.sup.2.times.s).
Some manufacturers of vacuum cleaners have even marketed bagless vacuum cleaners to avoid the cost of bags. However, this type of vacuum cleaner has less suction and the compartment holding the dust must be emptied manually. This largely nullifies its advantages by exposing the worker and the environment to the concentrated dust. Nevertheless, the bagless cleaner has prompted manufacturers to continue to improve the overall performance of bags.
The prior art addressed the problem of providing a vacuum cleaner bag with improved filtration efficiency. U.S. Pat. No. 5,080,702, Home Care Industries, Inc. discloses a disposable filter container-like bag which comprises an assembly of juxtaposed plies, namely an inner and outer ply of air pervious material. U.S. Pat. No. 5,647,881 (EPO 0 822.775 B1) discloses a three layer composite of an outer support layer, middle charged fibrous filter layer having specific properties and an inner diffusion layer unbonded except at least at one seam to the fibrous filter layer. The diffusion layer is described to provide the filter bag as its main function, with resistance to shock loading. EPO 0 338 479 to Gessner discloses a dust filter bag with a fibrillated fleece-lined outer layer of filter paper. The filtration grade fibrillated fleece layer is upstream of the filter paper.
The disclosures of the above mentioned patents are incorporated herein in their entirety by reference.
In the vacuum bag of the invention the principal function of the inner layer is that of high dust-holding capacity, a property of this magnitude not yet disclosed in the prior art.
It is desirable to have enhanced performance vacuum cleaner bag composite structures that can yield a high efficiency of up to 99.9% and also, allow a high flow with minimal pressure gradient increase measured by the DIN 44956-2 test.
A primary object of this invention is to provide a novel vacuum cleaner bag composition capable of extremely high filtration efficiency to fine dust and of maximum performance of a vacuum cleaner in terms of continuous high suction for picking up dust without a notable increase in pressure drop until the bag is filled.
A second objective of this invention is to provide a bag with a composition such that it has the rigidity needed for it to be fabricated and shaped on conventional vacuum cleaner bag making equipment.
A third objective of this invention is to construct a vacuum cleaner bag media that by virtue of its excellent filtration efficiency and superior non-blocking, high airflow performance, will be most suitable to the new European trend of small vacuum cleaners, with of course, smaller vacuum dust bags.
These and other objectives of this inventor will become apparent to one skilled in the art from the following disclosure.
The Nonwoven Fabrics Handbook of the Association, of the Nonwoven Fabrics Inductry, 1992, is incorporated herein in its entirety by reference.